The present invention relates to a vacuum and pressure tight ventilating or cooling device, specifically designed for thermoforming stations.
The invention also relates to a thermoforming station provided with the mentioned device.
More specifically, the thermoforming stations the invention is related to are conventionally provided for molding a sheet-like (or plate or coil-like) plastic material by drawing this material inside a bell assembly arranged at a position opposite to a mold bearing assembly, so as to be closed on the latter.
In particular, in such a thermoforming station, the sheet-like plastic material is brought at first to its plasticizing temperature and then it is locked, in a molding position, by closing the mentioned bell assembly against a perimetrical edge of the plastic material.
Then, the inside of the bell assembly is evacuated to draw the plastic material into the bell assembly, in order to provide said plastic material with a pre-stretched ball configuration.
Then, a mold is arranged under the thus formed ball, and the vacuum direction is reversed so as to cause the plastic material to be pressed against the mold to receive the desired molded pattern.
Then, the plastic material as molded is allowed to cool, the bell assembly being constantly closed on the mold to hold the plastic material on the mold itself.
By the above mentioned molding method a lot of article of manufactures are made, such as bags, car components, cells and counter-doors for domestic refrigerators, bath articles and the like.
In the above mentioned method, the cooling step represents the most critical processing step since the outer surface of the molded article must be evenly cooled. In fact, if the outer surface would not be properly evenly cooled, it could retain inner stresses which could deform the molded article which would be rejected.
Moreover, the cooling step represents the longest operating step of the thermoforming process and, in order to increase the thermoforming process yield it would be indispensable to make the cooling stage as short as possible.
Accordingly, the main object of the present invention is to provide ventilating means specifically designed for aiding air to easily circulate inside the mentioned thermoforming stations.
According to one aspect of the present invention, the above mentioned object, as well as yet other objects, which will become more apparent hereinafter, are achieved by a cooling ventilating device which comprises a vacuum and pressure tight-cooling ventilating device for a thermoforming station, wherein said device comprises, operatively coupled to form an autonomous cooling unit to be coupled to said thermoforming station, a scroll body defining an air inlet and an air outlet, air flow linearly reciprocating shutter plate disk means arranged at said air inlet of said scroll body and a driving motor-fan assembly arranged at said air outlet of said scroll body, and piston means for reciprocating said shutter means from a first opening position, opening said air inlet of said scroll body, to a second vacuum and pressure closing position, tightly closing said air inlet.
The provision, on the inventive device, of a shutter element arranged outside the thermoforming station, provides the advantage that an air jet can be easily directed and oriented in the thermoforming station.
Moreover, said outer shutter element will facilitate the assembling operations, and will reduce the operating noise (since said shutter element will break the air flow) while reducing the size of the device, to allow a desired number of ventilating devices to be easily arranged about the bell assembly.
The device according to the invention, moreover, provides the additional advantage of easily shutting off or closing the ventilating device, and this by the mentioned shutter element operating with a return force directed in the direction of the vacuum formed inside the bell assembly.
Thus, the negative pressure formed in the thermoforming station will facilitate the closing of the shutter element, while properly holding it in this closing position.
Thus, the bell assembly evacuation time as well as the cooling time will be reduced to a minimum. In particular, the cooling time can be reduced, owing to the inventive device, to total time less than 20 seconds, thereby easily overcoming a threshold of 120 cycles/hours as conventionally provided in processes designed for making domestic refrigerators, cells and counter-doors.
Advantageously, moreover, the inventive device further provides a sealing action against a possible air. overpressure generated in the thermoforming station for aiding the thermoforming process.